This invention relates to a method for forming prestressed centrifugal piles, a mould for implementing the method, and a pile obtained by the method.
Methods are known for forming prestressed centrifugal piles of frusto-conical shape. One of these known methods uses two metal half-shells forming a mould inside which a reinforcement is placed consisting of a ring of steel strands of length slightly greater than the length of the mould, together with a spiral located on the outside of the strands.
In order to maintain the strand cross-section/pile cross-section ratio substantially constant, and thus prevent fracture of the concrete when subjected to non-uniform prestressing, it is known to progressively deviate the strands towards the mould interior, so that portions of them lie within the central cavity which is obtained during the subsequent centrifuging stage, or to cover end portions with a sheath. In this manner, although the strands extend over a length equal to the pile length, they do not adhere to the concrete beyond a certain point, and therefore do not transmit their load fraction thereto.
This method however has the drawback of a certain laboriousness due to the need to prepare the end portions of the strands.
In another known method, the reinforcement consists of strands of different lengths, secured to a spiral disposed on their inside.
This known method has the drawback that the hooping effect is lost, so that the pile has limited load resistance.
An object of the invention is to obviate the drawbacks of known methods, by providing a method for forming prestressed centrifugal piles of high load resistance.
A further object of the invention is to provide a method which enables the strands to be easily anchored within the mould.